Men may be able to drastically reduce their chances of developing prostate cancer by making sure they sleep better. This is the conclusion that epidemiologists at the University of Iceland draw from a study in which they monitored 2,102 men aged 67-96 for an average of five years.

Sleep
There are a couple of epidemiological studies which show that sleep protects men from prostate cancer. In 2008, Japanese researchers reported for example that men who got at least 9 hours' sleep a day contracted prostate cancer only half as often as men who had shorter nights. [Br J Cancer. 2008 Jul 8;99(1):176-8.]

Study
The Icelandic study was published in 2013 in Cancer Epidemiology, Biomarkers & Prevention and looked at the same relationship. Prostate cancer is often associated with urinary problems as a result of prostate enlargement, and men who already have prostate cancer sleep worse as a result. Therefore the researchers excluded from their sample all men who possibly were sleeping badly for this reason.

The researchers measured the men's sleep quality by getting them to fill in questionnaires. They asked the men whether they needed to take sleeping pills several times a week [Q1], whether they were still awake half an hour after going to bed several times a week [Q2], whether they had difficulty falling asleep after waking in the night several times a week [Q3] and whether they woke far too early in the morning and couldn't get back to sleep several times a week [Q4].

The researchers divided the participants into 4 groups according to their answers. How they did that is shown in the illegible figure below. Click on the figure for a larger version.

Results
At the end of the five years, 132 men had developed prostate cancer. The researchers discovered that mild sleeping problems raised the likelihood of prostate cancer, but the increase was not alarming for this kind of study. However, among men with very serious sleep problems, the chance of advanced prostate cancer was considerably higher. Advanced prostate cancer is incurable.

Men with serious sleep problems used sleeping pills several times a week, had more problems falling asleep several times a week, found it difficult to get back to sleep after waking during the night, and woke early in the morning while they still felt tired.